We've already covered some of the highlights in RM Auctions' forthcoming Classic Muscle & Modern Performance sale in San Diego on June 19, including not one but two L88 Corvettes and an exceptionally rare Chevrolet Chevelle SS LS6 "Earth Mover".

But, two weeks prior to its San Diego extravaganza, RM is also auctioning an exceptional collection featuring a wide range of 20th century automobiles from the former Pate Museum of Transportation in Cresson, Texas.

RM's sale will offer over 40 historic motor cars which have been in long-term ownership, and promises "some of the most significant and technically interesting" automobiles of the last century.

The 1903 Cadillac Model A Runabout

Rolling works of art in the auction include a vintage 1903 Cadillac Model A Runabout with Rear-entry Tonneau, one of the first ever Cadillacs on the road. It was powered by an improved engine designed by Henry Martyn Leland and partner Robert C Faulconer, two years previously.

In 1903, approximately 2,500 of these runabouts were built. This Model A was particularly noted for performing well on hill climbs and reliability trials, and gained wide acclaim at the time. The car's catalogue listing refers to its distinctive rear-entry tonneau coachwork (pictured below).

Henry Martyn Leland and Robert C Faulconer's improved engine (bottom)

This historically important automobile boasts a firmly established legacy, and will sell complete with a binder which includes photocopies of the original specifications and operating instructions.

Selling without reserve, the car carries an estimate of $50,000-75,000.

RM Auctions' sale of The Pate Collection will take place in Cresson, Texas on June 5.